Drugs, foods, sanitary products, living miscellaneous goods, sintered structural parts, electronic parts and semiconductors are among areas in which molded products are manufactured by pressing a variety of materials. While molded or semi-molded products in all these areas are manufactured by pressing molding materials into an intended shape, press systems are actually commonly different depending on characteristics of intended molded products and requested needs.
Molded products used for drugs, foods, sanitary products and living miscellaneous goods are relatively simple in shape, can be pressed at low pressures and further generally use rotary presses that can manufacture molded products at high speed out of needs for manufacturing an exceedingly large number of products at low cost. Rotary press, in which a plurality of dies are arranged on a turn table, with punches held thereabove and therebelow and in which the turn table is moved in the direction of rotation, manufactures molded products by continuous supply of molding materials, pressing and ejecting of molded products. Normally capable of manufacturing several thousands of molded products per minute, rotary presses mainly feature a remarkably high productivity as compared with stroke presses that will be discussed later.
On the other hand, stroke presses are chiefly employed for molded products in areas such as sintered structural parts, electronic parts and semiconductors that are more complicated in shape and require pressing at high pressures. As for stroke presses used in metal working areas including sintered structural parts, for example, pressurized cylinder type and eccentric cam type presses are generally used. These presses are designed to press-mold molding materials by moving punches held above and below a die in relative directions. Such presses are commonly characterized in using a single die to supply molding materials, press and eject molded products and allow, because of their simple structure, manufacture of molded products requiring pressing at high pressures, molded products in complicated shape using multipunch and molded products of extremely high precision. However, such presses are low in production efficiency due to the structure and press system thereof and therefore not suited for mass production—disadvantages as compared with rotary presses.
In stroke presses, pairing of a die and punches can be generally broadly divided into stationary die-movable lower punch system and stationary lower punch-movable die system—a system generally called withdrawal dieset. Similarly in press system, some use hydraulic or pneumatic cylinders to apply pressure while others employ a system such as CNC (Computer Numerical Control) equipped with an electronic controller, servo-driven ball screw, etc.
Also in rotary presses, methods for producing shapes of a certain degree of complexity have been disclosed in the case of a single molding material rather than a plurality of molding materials. Ring-shaped punches, as in the lower punch mechanism of the rotary powder compression molding machine recited in Japanese Unexamined Patent Application Publication No. 52-126577, are designed to ensure uniform bulk material density during molding by moving the lower center and outer punches separately and charging bulk material in accordance with the shape of the final molded product. However, since such multistructured punches—conventional so-called ring-shaped punches—are used to aid in charging of bulk material, no consideration has been given to manufacturing a molded product consisting of a plurality of molded parts.
Rotary press for press-coated tablets used in the area of drugs is among apparatuses for manufacturing molded products consisting of a plurality of molded parts. The manufacturing method for press-coated tablets using a rotary press for press-coated tablets is by manufacturing in advance core with a separate rotary press, feeding the coatings into the die of a rotary press for press-coated tablets supplied with an outer-layer bulk material and further feeding and press-molding the outer-layer bulk material. According to the method, it is possible to arrange different constituents at the center and on the outside. In the method for feeding coatings into the die, however, it is substantially impossible to feed a coating identical to the die inner diameter or accurately localize a plurality of coatings at specific positions because present rotary presses for press-coated tablets have difficulties accurately positioning a coating at the center of the die, and therefore it is extremely difficult to divert a rotary press for press-coated tablets for manufacturing non-coated molded products consisting of a plurality of molded parts.
On the other hand, in sintered structural parts or the so-called metallurgy area, a method for manufacturing a molded product containing a plurality of constituents in a localized manner has been disclosed in Japanese Unexamined Patent Application Publication No. 52-2817. The Publication recites a method (FIG. 2) for manufacturing a molded product in which different bulk materials are localized perpendicularly to the pressure application surface, as shown in FIGS. 1(A), 1(B) and 1(C) (it should be borne in mind that while the molded product in the Publication is in troche form with a hollow at the center and with a center pin provided for securing the hollow, the substantial form is the same as those shown in FIGS. 1 and 2). According to the method, multipunches are used for both the upper and lower punches, and one of the lower punches is lowered relative to the die first, and a powdered material is fed into a created space. Then, the upper punch corresponding to the lower punch is lowered to mold under pressure the powdered material between the lower punch, the die and the upper punch. Then, a lower punch different from the lower punch is lowered relative to the die, with the already molded powdered molded compact left in the mold hole. A powdered material different from the powdered material is supplied and then molded under pressure together with the temporary molded product to manufacture a molded product. Although the manufacturing method is assumably intended for a stroke press judging from the area, the method presents a number of manufacturing problems.
Thus, no prior art substantially exists since there is no method for manufacturing a non-press-coated molded product consisting of a plurality of molded parts as industry at present.
In medical workplaces, for example, where white round tablets are predominant, on the other hand, tablet identifiability is an important issue. The reason is that information such as product names, contents of principal agents and manufacturers must be discernible when tablets are in random orientations after being taken out of their packages, and such information is used for confirmation and other purposes in medicine preparation and when patients take medicines. Today, “tablet codes” (codes by combination of characters and graphics) has been introduced as a tablet identification method, and the Federation of Pharmaceutical Manufacturers' Associations of JAPAN (FPMAJ) has defined “the Identification Code Implementation Procedure for Tablets and Capsules” in the FPMAJ Issue 80 that is now practiced by pharmaceuticals manufacturers as a voluntary arrangement.
Tablet codes can be printed by printing characters and other information on the tablet surface by ink or engraved by pressing a punch of convex shape on the surface thereof against a molded product, compacting the tablet and thereby producing a concave engraved code on the tablet surface. Among these, the printing method has had a variety of problems including complication of steps, cost aspect, use of organic solvents and rigorous technical requirements in printing step such as “print deviation.”
On the other hand, the engraving method accounts for 70 to 80% of tablets on the whole. However, this method has problems such as difficulties in seeing codes, resulting in a hindrance to identifiability of tablet codes. As compared with tablet printing, nevertheless, engraving does not require tablet coating—a step necessary in printing. Additionally, engraving is simpler with less manufacturing steps, thus allowing manufacturing cost reduction. Further, engraving requires no use of organic solvents needed in printing, resulting in widespread use because of its freedom from printing problems such as “print deviation.”
While there may be a variety of reasons for difficult-to-see engraving, such a difficulty is commonly thought to be attributed to its form. Since engraving is intended, by producing a concave indentation on a monochrome tablet, to render the code legible with the shadow created by the indentation and the tablet surface, it is known that the code is less legible due to halation at a relatively bright location such as under a fluorescent lamp, making engraving obviously inferior in terms of identifiability to printing in which characters are clearly discernible by color difference.
Many areas other than drugs produce molded products by compressing molding materials as well. In such molded products, characters and graphics are often added for the purpose of enhancing product added values, from design aspect, for trademark addition and so on. However, such molded products are commonly manufactured by the same manufacturing method as with the aforementioned tablets in drugs, thus entailing the same problems.